"The greatest trade of the year had to be the Kennedy family. They somehow traded Arnold Schwarzenegger for Taylor Swift," Paisley joked about Swift dating the 65-year-old bodybuilder's nephew through marriage. "I mean, what they got for that . . ."

But Underwood (married to NHL hunk Mike Fisher since 2010) interrupted her co-host to inform him of Swift's breakup. "What? Why don't I ever hear about these things?" Paisley asked. "I'm the last one to know. Are they ever gonna get back together?"

Swift is set to open the Grammys show at L.A.'s Staples Center Sunday. "What's interesting is we presented this performance to the Grammy committee . . . and they said, 'Okay, cool, you have a performance spot.' And then like a week ago they call us and are like, 'Oh, by the way, you're opening the show,'" Swift toldRyan Seacrest Thursday, Feb. 7. "It's not like they approach you . . . It just surprised me I was going to go first."